Vehicle evaporative emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of undesired evaporative emissions that could release fuel vapors to the atmosphere.
Undesired evaporative emissions may be identified using engine-off natural vacuum (EONV) during conditions when a vehicle engine is not operating. In particular, a fuel system and evaporative emissions control system may be isolated at an engine-off event. The pressure in such a fuel system and evaporative emissions control system will increase if the tank is heated further (e.g., from hot exhaust or a hot parking surface) as liquid fuel vaporizes. If the pressure rise meets or exceeds a predetermined threshold, it may be indicated that the fuel system and the evaporative emissions control system are free from undesired evaporative emissions. Alternatively, if during the pressure rise portion of the test the pressure curve reaches a zero-slope prior to reaching the threshold, as fuel in the fuel tank cools, a vacuum is generated in the fuel system and evaporative emissions system as fuel vapors condense to liquid fuel. Vacuum generation is monitored and undesired emissions identified based on expected vacuum development or expected rates of vacuum development. The EONV test may be monitored for a period of time based on available battery charge.
However, the EONV test is prone to false failures based on customer driving and parking habits. For example, a refueling event that fills the fuel tank with relatively cool liquid fuel followed by a short ensuing trip may fail to heat the fuel bulk mass and may result in a false fail if an EONV test is run. Further, the rates of pressure build and vacuum development are based in part on the ambient temperature. During mild weather conditions, the ambient temperature may restrict the amount of heating or cooling of the fuel tank following engine shut-off, and thus limit the rate of pressure or vacuum development. As such, in a case wherein a pressure build does not reach the expected threshold, the subsequent vacuum build may additionally not reach expected threshold level in the time allotted for the EONV test based on available battery charge. This may result in a false-fail condition, leading to potentially unnecessary engine service. The inventors herein have recognized these disadvantages.
U.S. Pat. No. 6,314,797 teaches sealing an evaporative emissions control system at a key-off event and monitoring a vacuum switch coupled to the evaporative emissions control system for a closing event due to a natural vacuum created in the evaporative emissions control system as it cools. If a closing event is not detected, it is determined whether a timer has exceeded a predetermined threshold value, and is so, the presence of undesired evaporative emissions are indicated. In one example, it is taught that diurnal temperature cycling may result in the formation of a vacuum-build in the sealed fuel system and evaporative emissions control system, and if the vacuum switch is closed under such conditions, then it may be indicated that the fuel system and evaporative emissions control system are free from undesired evaporative emissions. However, the inventors herein have recognized potential issues with such systems. As one example, a vehicle which is primarily driven at night, and which is thus primarily parked during the day, may only experience heat gains during times when the vehicle is in a prolonged key-off condition, and thus the vacuum switch may never close. In such an example of vehicle operation, in-use monitoring performance (JUMP) rates may be significantly impacted. Furthermore, the use of a vacuum switch may require an application specific integrated circuit (ASIC) chip to be alive at all times in a low power mode in order to sense that the vacuum switch is closed from a diurnal cycle cooldown. The use of such a chip can affect the main battery drain. Ideally, a controller would only be woken up at an opportune time for conducting an evaporative emissions test diagnostic procedure, where an opportune time may comprise portions of the diurnal cycle where heat gains and losses are greatest.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising routing fuel vapors from a fuel tank in a fuel system to an evaporative emissions control system, the fuel system supplying fuel to an engine which propels a vehicle; conducting an evaporative emissions test diagnostic procedure of the fuel system and the evaporative emissions control system; and adjusting timing of the evaporative emissions test diagnostic procedure responsive to detection of an ambient light amount.
As one example, the evaporative emissions test diagnostic procedure occurs during a vehicle-off condition, and includes maintaining a controller of the vehicle in a sleep mode during the vehicle-off condition, waking the controller based on the ambient light amount, and returning the controller to sleep mode responsive to completion of the evaporative emissions test diagnostic procedure. In one example, the ambient light amount may be based on output from a solar cell configured on an external surface of the vehicle. As such, the ambient light amount may be related to an ambient temperature increase or an ambient temperature decrease during the course of a diurnal temperature cycle, wherein the ambient light amount includes a change in ambient light greater than a threshold that results in initiation of the evaporative emissions test diagnostic procedure. In this way, the evaporative emissions test diagnostic procedure may be conducted during either a transition from dark-to-sunlight hours (sunrise), or from sunlight-to-dark (sunset) hours. Enabling the evaporative emissions test diagnostic procedure to execute at either sunrise or sunset is an advantage over other prior art methods which make use of a vacuum switch to detect undesired evaporative emissions based on the diurnal temperature cycle. By enabling the evaporative emissions test diagnostic to execute at either sunrise or sunset events, both a pressure increase and a vacuum build may be utilized to infer the presence or absence of undesired evaporative emissions, in contrast to only relying on a vacuum build. As such, in use monitoring performance completion rates may be improved. Furthermore, by sleeping the controller during vehicle-off conditions, and only waking the controller responsive to a change in ambient light amount greater than a threshold, main battery drain may be reduced.
In another example, a method is provided, comprising routing fuel vapors from a fuel tank in a vehicle fuel system to an evaporative emissions control system which is coupled to atmosphere, the fuel tank supplying fuel to an engine which propels a vehicle and responsive to an indication of a vehicle-off event: in a first condition, maintaining a controller of the vehicle awake and conducting an engine off natural vacuum (EONV) test of the fuel system and the evaporative emissions control system; and in a second condition, sleeping the controller and searching for an indicated change in ambient light amount greater than a threshold, waking the sleeping controller when the indicated change in ambient light amount is greater than a threshold, and conducting an evaporative emissions test diagnostic procedure of the fuel system and the evaporative emissions control system in response to the waking of the controller.
As one example the method includes determining a heat rejection index, wherein the heat rejection index is based on an amount and/or timing of heat rejected by the engine for an engine run time duration prior to the vehicle-off event; wherein the first condition comprises the heat rejection index above a threshold; and wherein the second condition comprises the heat rejection index below the threshold. In this way, by determining at the vehicle-off condition whether to conduct an EONV test or whether to conduct an evaporative emissions test diagnostic procedure based on a change in ambient light amount, in use monitoring performance (IUMP) rates for checking the fuel system and evaporative emissions control system for the presence of undesired evaporative emissions may be increased without affecting main battery drain.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.